Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Department of Ecohydrology, Justus von Liebig Straße 7, 12489 Berlin, Germany; Humboldt-University Berlin, Geography Department, Unter den Linden 6, 10099 Berlin, Germany.
Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Department of Ecohydrology, Justus von Liebig Straße 7, 12489 Berlin, Germany.
Sci Total Environ. 2018 Jul 15;630:1515-1527. doi: 10.1016/j.scitotenv.2018.02.070. Epub 2018 Mar 7.
In Brazil, a steady increase in phosphorus (P) fertilizer application and agricultural intensification has been reported for recent decades. The concomitant P accumulation in soils potentially threatens surface water bodies with eutrophication through diffuse P losses. Here, we demonstrated the applicability of a soil type-independent approach for estimating the degree of P saturation (DPS; a risk parameter of P loss) by a standard method of water-soluble phosphorus (WSP) for two major soil types (Oxisols, Entisols) of the São Francisco catchment in Brazil. Subsequently, soil Mehlich-1P (M1P) levels recommended by Brazilian agricultural institutions were transformed into DPS values. Recommended M1P values for optimal agronomic production corresponded to DPS values below critical thresholds of high risks of P losses (DPS=80%) for major crops of the catchment. Higher risks of reaching critical DPS values due to P accumulation were found for Entisols due to their total sorption capacities being only half those of Oxisols. For complementary information on soil mineralogy and its influence on P sorption and P binding forms, Fourier transformation infrared (FTIR) spectroscopic analyses were executed. FTIR analyses suggested the occurrence of the clay minerals palygorskite and sepiolite in some of the analyzed Entisols and the formation of crandallite as the soil specific P binding form in the investigated Oxisols. Palygorskite and sepiolite can enhance P solubility and hence the risk of P losses. In contrast, the reshaping of superphosphate grains into crandallite may explain the chemical processes leading to previously observed low dissolved P concentrations in surface runoff from Oxisols. To prevent high risk of P losses, we recommend avoiding superficial fertilizer application and establishing environmental thresholds for soil M1P based on DPS. These measures could help to prevent eutrophication of naturally oligotrophic surface waters, and subsequent adverse effects on biodiversity and ecosystem function.
在巴西，近几十年来，磷 (P) 肥料的应用和农业集约化一直在稳步增加。与此同时，土壤中磷的积累有可能通过扩散磷的损失威胁到地表水的富营养化。在这里，我们通过一种标准的水溶性磷 (WSP) 方法，证明了一种土壤类型独立的方法来估计磷饱和度 (DPS；一种磷损失风险参数) 的适用性，该方法适用于巴西圣弗朗西斯科流域的两种主要土壤类型（氧化土、淋溶土）。随后，将巴西农业机构推荐的土壤 Mehlich-1P (M1P) 水平转化为 DPS 值。对于流域主要作物来说，最佳农业生产推荐的 M1P 值对应于低于高磷损失风险（DPS=80%）临界阈值的 DPS 值。由于 Entisols 的总吸附能力仅为 Oxisols 的一半，因此由于磷积累而导致达到临界 DPS 值的风险更高。傅里叶变换红外 (FTIR) 光谱分析为补充土壤矿物学及其对磷吸附和磷结合形式的影响提供了信息。FTIR 分析表明，在一些分析的淋溶土中存在粘土矿物坡缕石和海泡石，并且在所研究的氧化土中形成了铬明矾作为土壤特有的磷结合形式。坡缕石和海泡石会增加磷的溶解度，从而增加磷损失的风险。相比之下，过磷酸钙颗粒重塑成铬明矾可以解释导致先前观察到氧化土地表径流中溶解磷浓度较低的化学过程。为了防止磷损失的高风险，我们建议避免表面施肥，并根据 DPS 为土壤 M1P 建立环境阈值。这些措施有助于防止贫营养化地表水的富营养化，以及对生物多样性和生态系统功能的后续不利影响。
